The present invention relates to a water treatment apparatus for a fuel cell system. In particular, the present invention relates to a water treatment apparatus which continually removes iron oxide, dissolved carbon dioxide, organic material, and trace ions generated in the water system of a phosphoric acid fuel cell electric power plant, without relying on the use of added chemicals. The present invention also relates to a water treatment apparatus that recycles treated water for use as cooling water for the body of the fuel cell system.
Referring to FIG. 2, there is shown a flow diagram of a conventional small size phosphoric acid fuel cell system 1. A fuel cell 5 has an anode 3, a cathode 4, and an electrolyte 2. A cooling unit 6 which cools fuel cell 5 is placed inside a fuel cell body 7.
Fuel such as natural gas or the like is brought in by a pipe 10. Inside a reformer 11, this gas is reformed into a hydrogen-rich gas by steam brought in from a steam separator 23 via a pipe 12. Air is brought into reformer 11 by pipes 13, 13A to effect combustion. Reformer 11 also has unreacted fuel (hydrogen-rich exhaust gas from the anode) brought in by a pipe 14, and this becomes the heat source for the reform reaction. After its carbon monoxide component is transformed in a transformer 15, the reformed gas is brought to anode 3 by a pipe 16. The combustion exhaust gas of reformer 11 is sent to a condenser 19 by pipes 17, 18.
At cathode 4, air is brought in via pipes 13, 13B. The reformed gas brought to anode 3 is oxidized by an electrochemical reaction using this air, and electricity is generated. Exhaust gas from cathode 4 is sent to condenser 19 by pipes 18, 20.
The separated water from steam separator 23 is sent to cooling unit 6 as cooling water via pipe 24. Cooling water which has been heated by cooling unit 6 is returned to steam separator 23 by a pipe 27. This forms the cell body cooling water system. Treated water from water treatment apparatus 22 is delivered as needed by a pipe 25 to the cooling water system as make-up water.
The condensate separated in condenser 19 (hereinafter referred to as exhaust gas condensate) is sent to water treatment apparatus 22 via a pipe 21. Blowdown water from the cell body cooling system is brought to water treatment apparatus 22 by a pipe 29 from a heat exchanger 28. Exhaust gas is discharged outside the system by a pipe 19A.
In this relatively small scale phosphoric acid fuel cell system, the exhaust gas condensate from condenser 19 includes many impurities and contaminants. These impurities and contaminants include carbon dioxide, which is generated in reformer 11 and transformer 15, phosphate, iron, and the like. Similarly, the blowdown water from steam separator 23 also has iron and other impurities. Furthermore, because carbon steel pipes are usually used for the system piping of a fuel cell generator plant, the water recovered in water treatment apparatus 22 also contains a large amount of iron oxide and iron ions.
To achieve good electrical insulation and corrosion prevention in the cooling water system, the cooling water supplied to cooling unit 6 of fuel cell system 1 must have a low electroconductivity. For this reason, exhaust gas condensate from condenser 19 and blowdown water from the cell body cooling water system are recovered and treated by water treatment apparatus 22, which supplies the cell body cooling water system. Water treatment apparatus 22 is needed to remove impurities from the recovered water, and reduces ions to a sufficiently low concentration.
In a conventional water treatment device 22 of a fuel cell system, the recovered water is first passed through a mesh strainer, and any impurities are removed. Next, the water is passed through an activated carbon column to remove any organic materials. Finally, ions are removed by an ion exchange resin.
In a conventional water treatment apparatus, the mesh strainer quickly becomes clogged, due to the iron oxide in the recovered water. The activated carbon column in the following step also clogs quickly. Therefore, these must be replaced frequently. Furthermore, the iron ions not removed by the activated carbon column and remaining in the outflow water from the activated carbon column coat the surface of the ion exchange resin in the last step. Because of this, and because the recovered water is at a relatively high temperature (45.degree. C.), degradation of the ion exchange resin is rapid, and the ion exchange resin must also be frequently replaced.
Because of the need to replace the mesh strainer, the activated carbon column, and the ion exchange resin frequently, the operating efficiency and processing efficiency of these systems are low. Therefore, the operating cost of water treatment by these systems is high.
To solve this problem, a large scale decarbonation column is used for decarbonation treatment. A strong oxidant such as chloride ion or the like is added in order to completely oxidize any iron ions in the recovered water. After removing these by coagulation filtration or the like, any remaining ions must still be removed by an ion exchange resin. As a result, the equipment becomes large and complex. The use of added chemicals further increases the costs.